An experiment was carried out during 120 days in 1995 at the experimental farm of
Cantho University using 24 pigs (Yorkshire X Landrace-Baxuyen) allotted in a completely
randomized design with two treatments and three replications. The pigs had an average
initial liveweight of 25.8 kg and were fed (ECR) ensiled cassava root and duckweed (Lemna
spp) with a protein supplement or (control) a concentrate diet based on rice
by-products.

There were no significant differences in daily weight gain or feed conversion
between treatments. The pigs fed ensiled cassava root and duckweed had thinner back-fat as
compared with control pigs (P= 0.002).

It is concluded that a diet based on ensiled cassava root and with duckweed (Lemma
spp) replacing part of the protein supplement can replace the rice by-products
traditionally used to fatten pigs in Vietnam.

Key words: Pigs, ensiled cassava root, duckweed, fattening

Introduction

The Mecong delta, with a large acid-sulphate soil area, is the major rice-producing
region in Vietnam. It also has good potential for growing sugar cane and cassava and the
extensive water surfaces create opportunities for cultivation of water plants, especially
water spinach (Ipomoea aquatica) and duckweed (Lemna spp).

Previous research in Vietnam, on making better use of local feed resources was
with by-products of sugar cane, showed that AA@ molasses and crude sugar could replace completely
cereal grain products in the diets of fattening and breeding pigs (Bui Hong Van and Le Thi
Men 1990; Bui Hong Van and Le Thi Men 1992; Bui Huy Nhu Phuc and Luu Trong Hieu 1993; Bui
Huy Nhu Phuc 1995).

The aims of the present study were:

To compare a diet based on ensiled cassava root with the conventional diet of cereal
grains and cereal by-products for fattening pigs

Evaluate the use of duckweed as partial replacement for the conventional protein
supplements.

Materials and methods

The trial was conducted at the experimental farm of Cantho university from April to
July 1995 and lasted for 120 days. The experimental animals were 24 crossbred pigs
(Yorkshire X Landrace-Baxuyen) aged 3 months and with a mean live weight of 25.8 kg. The
experimental design was a randomized block consisting of 2 treatments and 3 replications.

The composition of the experimental diets is shown in Table 1. The concentrate
used in the control diet contained broken rice 60, rice bran 33, Soya bean meal 2 and
fishmeal 5. The ensiling of the cassava roots was done using the procedure described
earlier (Le Thi Men et al 1997). Whole cassava roots were washed, chopped to thin chips
and raw sugar added at the rate of 5%. The time of ensiling was 3 weeks. The duckweed was
grown in earth-lined ponds fertilized with biodigester effluent as described by Bui Xuan
Men et al (1996).

Mean values for growth, feed intake and conversion are in Table 2. There were
indications (P=0.08) that the pigs fed the diet based on rice by-products had slightly
(5%) higher growth rates than those fed the ensiled cassava root diet. Conversion rates
were similar for both treatments. The pigs fed ensiled cassava root and duckweed had
thinner back-fat as compared with control pigs (P= 0.002).

Little work appears to have been done on the feeding of duckweed to fattening pigs
perhaps because emphasis in earlier studies was on producing a dry meal rather than
developing a system to use the freshly harvested duckweed. Also the use of fertilizer or
biodigester effluent to raise the protein and decrease the fibre level was perhaps not
understood. Thus, in an experiment with a low protein/high fibre duckweed meal (23% N*6.25
and 7.5% fibre in DM) pig growth was reduced by 30% over 40 days when there was 10% of
duckweed meal in the diet (Haustein et al 1992). In contrast, in a parallel study to the
present one, the replacement of 50% of a conventional protein source (fish meal and soya
bean meal) with fresh duckweed in the diet of breeding sows led to bigger litter size,
improved rates of survival and heavier litter weights (Le thi Men et al 1996)

Rodriguez and Preston (1996) reported that when fresh duckweed was fed as the
only supplement to sugar cane juice, the digestibility of the total diet dry matter was
83% with duckweed supplying 45% of the diet dry matter. Protein (N*6.25) digestibility at
this level of duckweed was 73%. In both these latter studies the protein content of the
duckweed was over 30% in the dry matter.

Conclusions and Recommendations

It is concluded that a diet of ensiled cassava root with 25% of the protein provided by
fresh duckweed can totally replace rice by-products and protein meals in diets for
fattening pigs with no reduction in growth rate or conversion and with leaner carcasses.

Acknowledgements

This research was supported by the International Foundation of Science through a grant
(B/2232-1) to Ms Le Thi Men.

References

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Bui Hong Van and Le Thi Men 1992 Feeding of sugar cane juce and
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Bui Hong Van and Le Thi Men 1990 A molasses in diets for growing
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Bui Huy Nhu Phuc 1993 The use of sugar cane juice and molasses in
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